#include <fstream>
#include <cmath>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bool a[100000];
int b[48000],p,u,i,j,n,nr,ma,ii,pp,nrdiv,nrr,r;
int main()
{
     f>>u;
    for (i=3;i*i<=u;i+=2)
        for (j=i*i;j<=u;j+=i)
             a[j]=1;

       b[2]=1;
      for (i=3;i<=u;i++)
       if (a[i]==0 && i%2)
         b[i]=b[i-1]+1;
        else
         b[i]=b[i-1];
        g<<b[u];

   f.close();
   g.close();
}